Method and system for pixel-wise imaging

ABSTRACT

There is provided a method and system for pixel-wise imaging of a scene. The method including: receiving a pixel-wise pattern, the pixel-wise pattern including a masking value for each pixel in an array of pixels of an image sensor; producing an electronic signal at each pixel when such pixel is exposed to light received from the scene; and directing the electronic signal at each pixel to one or more collection nodes associated with such pixel based on the respective masking value, the one or more collection nodes each capable of integrating the received electronic signal.

GOVERNMENT INTEREST

This invention was made with government support under HR0011-6-2-0021awarded by the Defense Advanced Research Projects Agency (DARPA). Thegovernment has certain rights in the invention.

TECHNICAL FIELD

The following relates generally to imaging, and more specifically, to amethod and system for pixel-wise imaging.

BACKGROUND

Imaging sensors, such as those found in still-cameras and video-cameras,have a plurality of photosensitive receptors. Typically, the receptorsare a Complementary Metal Oxide Semiconductor (CMOS) device. Photons oflight are collected on photosites of the receptors, typically there isone photosite for each pixel. Typically, the photons are directed at thephotoreceptors of the imaging sensor via one or more lenses. Anelectrical charge is produced in the silicon of the receptor for thatphotosite, where the charge is proportional to the intensity of thelight received. The value of each charge is turned into a digital valueby an analogue-to-digital converter.

For conventional colour imaging sensors, a quarter of the photositesrecord red light, another quarter record blue light, and the remaininghalf record green light. Typically, this filtering of light to eachphotosite is achieved by placing a coloured filter on each respectivephotosite, referred to as a Bayer filter array. Each of the colourpixels are interpolated, via a mosaic operation, with colour data inneighbouring photosites to assign a full colour value to each pixel.

Typically, when a conventional aperture is opened, all thephotoreceptors receive light at the same time, which means that eachpixel contributes approximately equally to the image. In other cases,there may be a rolling shutter, that successively blocks some photonsfrom reaching the imaging sensor; thus, providing temporal scanningacross the imaging sensor, either vertically or horizontally. Theselectivity of the photosites coming from which set of photosites arecollectively being blocked by the shutter at a certain instant.

It is therefore an object of the present invention to provide a methodand system in which the conventional disadvantages are obviated ormitigated, and attainment of desirable attributes is facilitated.

SUMMARY

In an aspect, there is provided a system for pixel-wise imaging of ascene, the system comprising: an image sensor comprising an array ofpixels, each pixel comprising a photosensitive receptor that produces anelectronic signal when exposed to light received from the scene; asignal storage module comprising one or more collection nodes for eachpixel, each collection node capable of integrating the electronic signalreceived by the respective photosensitive receptor; and a control logicmodule comprising control memory and one or more logic components, thecontrol memory receiving a pixel-wise pattern, the pixel-wise patterncomprising a masking value for each pixel of the image sensor, and foreach of the pixels, the one or more logical components directing theelectronic signal to one or more of the respective collection nodesbased on the respective masking value.

In a particular case, the one or more collection nodes comprises exactlytwo collection nodes per pixel, wherein the masking value is a one-digitbinary value, and wherein a high binary value indicates directing theelectronic signal to one of the collection nodes and a low binary valueindicates directing the electronic signal to the other collection node.

In another case, the one or more collection nodes comprises exactly fourcollection nodes per pixel, wherein the masking value is a two-digitbinary value, each of the four collection nodes associated with one ofthe two-digit binary values, and wherein the one or more logicalcomponents directs the electronic signal to the respective collectionnode based on the respective two-digit binary value.

In yet another case, the control memory receives a new pixel-wisepattern for every frame, and the one or more logical components directthe electronic signal based on the masking value of the new pixel-wisepattern.

In yet another case, the control memory receives a new pixel-wisepattern for every subframe, and the one or more logical componentsdirect the electronic signal based on the masking value of the newpixel-wise pattern, each frame comprising a plurality of subframes.

In yet another case, the control memory comprises a first memory unitand a second memory unit, the second memory unit storing the pixel-wisepattern for a current subframe and the first memory unit storing the newpixel-wise pattern for an upcoming subframe.

In yet another case, the new pixel-wise pattern for the upcomingsubframe is loaded into the first memory sequentially, and thepixel-wise pattern for the current subframe is loaded into the secondmemory simultaneously.

In yet another case, the image sensor comprises one of apinned-photodiode, a photo-gate, a charge-coupled device, a chargeinjection device, or a single photon avalanche diode.

In yet another case, the logical components comprise charge transfergates and the collection nodes comprise floating diffusion nodes.

In yet another case, the system further comprising a digitization moduleto digitize and output a measure of the integration at each collectionnode.

In yet another case, the imaging sensor is a line sensor.

In yet another case, the light received from the scene comprisestemporally modulated light from a light source and the one or morecollection nodes comprises exactly two collection nodes for each pixel,the system further comprising a processor to determine time-of-flight ofthe modulated light by measuring phase differences between the modulatedlight at the light source and the light received at the photosensitivereceptor, the one or more logical components directing the electronicsignal to one of the collection nodes during a first portion of themodulation of the modulated light and directing the electronic signal tothe other collection node during a second portion of the modulation ofthe modulated light.

In yet another case, the predetermined path type is selected from agroup consisting of a direct light path, an indirect light path, or aspecular light path.

In yet another case, the one or more collection nodes comprises exactlytwo collection nodes for each pixel, the system further comprising aprojector to project a light-pattern onto the scene, the pixel-wisepattern comprising a complementary pattern such that the one or morelogical components direct the electronic signal to one of the collectionnodes if the associated light received at the respective pixelapproximately comprises a predetermined path type, otherwise the one ormore logical components direct the electronic signal to the othercollection node.

In yet another case, the one or more collection nodes comprises exactlyone collection node for each pixel, the system further comprising aprojector to project a light-pattern onto the scene, the pixel-wisepattern comprising a complementary pattern such that the one or morelogical components direct the electronic signal to the collection nodeif the associated light received at the respective pixel approximatelycomprises a predetermined path type, otherwise the one or more logicalcomponents blocks or ignores the electronic signal, the predeterminedpath type is selected from a group consisting of a direct light path, anindirect light path, or a specular light path.

In yet another case, the light received from the scene comprisesphotometric stereo light illumination conditions from a light source andthe one or more collection nodes comprises exactly two collection nodesfor each pixel, the one or more logical components directing theelectronic signal to one of the collection nodes during a firstillumination condition and directing the electronic signal to the othercollection node during a second illumination condition, the systemfurther comprising a processor to determine normals of one or moreobjects in the scene via determining intensity of light received at eachpixel.

In yet another case, the normals are determined using intensitydemosaicing of two or more neighboring pixels.

In yet another case, the normals are determined using demosaicing with aratio of each pixel's collection nodes for two or more neighboringpixels.

In yet another case, the light received from the scene comprisesstructured light illumination conditions from a light source and the oneor more collection nodes comprises exactly two collection nodes for eachpixel, the one or more logical components directing the electronicsignal to one of the collection nodes during a first illuminationcondition and directing the electronic signal to the other collectionnode during a second illumination condition, the system furthercomprising a processor to determine depth to one or more objects in thescene from intensity of light received at each pixel via triangulationwith pixels at the light source and pixels at the image sensor.

In yet another case, the depths are determined using intensitydemosaicing of two or more neighboring pixels.

In yet another case, the depths are determined using demosaicing with aratio of each pixel's collection nodes for two or more neighboringpixels.

In another aspect, there is provided a method for pixel-wise imaging ofa scene, the method comprising: receiving a pixel-wise pattern, thepixel-wise pattern comprising a masking value for each pixel in an arrayof pixels of an image sensor; producing an electronic signal at eachpixel when such pixel is exposed to light received from the scene; anddirecting the electronic signal at each pixel to one or more collectionnodes associated with such pixel based on the respective masking value,the one or more collection nodes each capable of integrating thereceived electronic signal.

In a particular case, the one or more collection nodes comprises exactlytwo collection nodes per pixel, wherein the masking value is a one-digitbinary value, and wherein a high binary value indicates directing theelectronic signal to one of the collection nodes and a low binary valueindicates directing the electronic signal to the other collection node.

In another case, the one or more collection nodes comprises exactly fourcollection nodes per pixel, wherein the masking value is a two-digitbinary value, each of the four collection nodes associated with one ofthe two-digit binary values, and wherein the electronic signal isdirected to the respective collection node based on the respectivetwo-digit binary value.

In yet another case, a new pixel-wise pattern is received for everyframe, and the the electronic signal is directed based on the maskingvalue of the new pixel-wise pattern.

In yet another case, a new pixel-wise pattern is received for everysubframe, and the electronic signal is directed based on the maskingvalue of the new pixel-wise pattern, each frame comprising a pluralityof subframes.

In yet another case, the method further comprising storing thepixel-wise pattern for a current subframe and storing the new pixel-wisepattern for an upcoming subframe separately.

In yet another case, the new pixel-wise pattern for the upcomingsubframe is loaded into memory sequentially, and the pixel-wise patternfor the current subframe is loaded into memory simultaneously.

In yet another case, the method further comprising digitizing andoutputting a measure of the integration at each collection node.

In yet another case, the light received from the scene comprisestemporally modulated light and the one or more collection nodescomprises exactly two collection nodes for each pixel, the methodfurther comprising determining time-of-flight of the modulated light bymeasuring phase differences between the modulated light at the lightsource and the received light, and wherein directing the electronicsignal at each pixel comprises directing the electronic signal to one ofthe collection nodes during a first portion of the modulation of themodulated light and directing the electronic signal to the othercollection node during a second portion of the modulation of themodulated light.

In yet another case, the one or more collection nodes comprises exactlytwo collection nodes for each pixel, the method further comprisingprojecting a light-pattern onto the scene, the pixel-wise patterncomprising a complementary pattern such that the electronic signal isdirected to one of the collection nodes if the associated light receivedat the respective pixel approximately comprises a predetermined pathtype, otherwise the electronic signal is directed to the othercollection node.

In yet another case, the predetermined path type is selected from agroup consisting of a direct light path, an indirect light path, or aspecular light path.

In yet another case, the one or more collection nodes comprises exactlyone collection node for each pixel, the method further comprisingprojecting a light-pattern onto the scene, the pixel-wise patterncomprising a complementary pattern such that the electronic signal isdirected to the collection node if the associated light received at therespective pixel approximately comprises a predetermined path type,otherwise the electronic signal is blocked or ignored, the predeterminedpath type is selected from a group consisting of a direct light path, anindirect light path, or a specular light path.

In yet another case, the light received from the scene comprisesphotometric stereo light illumination conditions and the one or morecollection nodes comprises exactly two collection nodes for each pixel,the electronic signal is directed to one of the collection nodes duringa first illumination condition and the electronic signal is directed tothe other collection node during a second illumination condition, themethod further comprising determining normals of one or more objects inthe scene via determining intensity of light received at each pixel.

In yet another case, the normals are determined using intensitydemosaicing of two or more neighboring pixels.

In yet another case, the normals are determined using demosaicing with aratio of each pixel's collection nodes for two or more neighboringpixels

In yet another case, the light received from the scene comprisesstructured light illumination conditions and the one or more collectionnodes comprises exactly two collection nodes for each pixel, theelectronic signal is directed to one of the collection nodes during afirst illumination condition and the electronic signal is directed tothe other collection node during a second illumination condition, themethod further comprising determining depth to one or more objects inthe scene from intensity of light received at each pixel viatriangulation with pixels at the light source and pixels at the imagesensor.

In yet another case, the depths are determined using intensitydemosaicing of two or more neighboring pixels.

In yet another case, the depths are determined using demosaicing with aratio of each pixel's collection nodes for two or more neighboringpixels.

These and other embodiments are contemplated and described herein. Itwill be appreciated that the foregoing summary sets out representativeaspects of systems and methods to assist skilled readers inunderstanding the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention will become more apparent in the followingdetailed description in which reference is made to the appended drawingswherein:

FIG. 1 is a schematic diagram of a system for pixel-wise imaging of ascene, in accordance with an embodiment;

FIG. 2A is an example of the system of FIG. 1 of 1-bit coded exposureimaging masks applied over multiple subframes;

FIG. 2B is an exemplary pixel timing diagram for the system of FIG. 1with signal integration that depends on a masking bit value overmultiple subframes;

FIG. 3 is an exemplary embodiment of a control logic module for thesystem of FIG. 1 for one pixel;

FIG. 4 is an exemplary flow diagram for a two-bucket implementation ofthe system of FIG. 1 for one pixel;

FIG. 5 is an exemplary circuit implementation of the system of FIG. 1for a pixel array;

FIG. 6 is a waveform diagram for the circuit implementation of FIG. 5;

FIG. 7 is an example of a transistor-level implementation of atwo-bucket photonic mixing device and readout blocks of FIG. 3 for onepixel;

FIG. 8A is an example of a photo-detecting and mixing structure within apixel layout for the system of FIG. 1 with two storage nodes;

FIG. 8B is an example of a photo-detecting and mixing structure within apixel layout for the system of FIG. 1 with ‘k’ number of storage nodes;

FIG. 9 is an exemplary diagrammatic top view of a pixel layout for thesystem of FIG. 1 with two storage nodes;

FIG. 10 is an exemplary cross-section of an implementation of the pixelof FIG. 9;

FIG. 11 is a signal waveform diagram of the implementation of the systemin FIG. 1, using the pixel in FIG. 9;

FIG. 12 is a diagrammatic top view of another implementation of onepixel in the system of FIG. 1 for time-of-flight applications;

FIG. 13 is an exemplary timing diagram of the implementation of FIG. 12;

FIG. 14 is an exemplary embodiment of an architecture for variouscomponents of the system of FIG. 1;

FIG. 15 is another exemplary embodiment of an architecture for variouscomponents of the system of FIG. 1;

FIG. 16 is another exemplary embodiment of an architecture for variouscomponents of the system of FIG. 1 where loading circuitry are on bothsides of a pixel array to improve speed;

FIG. 17 is an exemplary diagram of a line (1D) image sensor architecturefor various components of the system of FIG. 1.

FIG. 18 is an exemplary embodiment of overall architecture of the systemof FIG. 1;

FIG. 19 is a diagram representing two states of a two bucket pixel forthe system of FIG. 1;

FIG. 20 is another exemplary timing diagram of the system of FIG. 1;

FIG. 21 is a diagrammatic illustration of an example code matrix;

FIG. 22 is an example diagram of a result of light transport to twobuckets for the system of FIG. 1;

FIG. 23 is an example illustration of images captured and mosaicsdetermined in accordance with the system of FIG. 1;

FIG. 24A is a chart comparing several combinations of approaches inaccordance with the system of FIG. 1;

FIG. 24B is a chart comparing a baseline 3-frame approach and a colorphotometric stereo approach considering the effect of spatial albedovariations in accordance with the system of FIG. 1;

FIG. 25A is a visualization of exemplary results of the system of FIG. 1used for structured light;

FIG. 25B is a visualization of exemplary results of the system of FIG. 1used for photometric stereo light;

FIG. 26 is a photo of the scene used for the results of FIGS. 25A and25B;

FIG. 27 shows a captured 3D map of a 1600 Lumen light bulb using aconventional camera and using the system 100 of FIG. 1;

FIG. 28 shows an image captured in bright sunlight with a conventionalcamera and with 3D imaging using the system of FIG. 1;

FIG. 29A shows an image captured using only direct light reflected onlyonce using the system of FIG. 1;

FIG. 29B shows that same scene of FIG. 29A except showing only indirectlight captured using the system of FIG. 1;

FIG. 30A shows an image captured of a latex glove by the system of FIG.1 capturing only indirect light;

FIG. 30B shows an image captured of a hand by the system of FIG. 1capturing only indirect light;

FIG. 31A shows a scene of ice blocks captured by a conventional camera;

FIG. 31B which shows a 3D image captured using conventionaltime-of-flight imaging of the scene of FIG. 31A;

FIG. 31C shows 3D imaging of the scene of FIG. 31A using the system ofFIG. 1 capturing direct-only light travel;

FIG. 32 illustrates an example of images captured using the system ofFIG. 1 showing images received in a first bucket and a determinednormal;

FIG. 33 illustrates an example of images captured using the system ofFIG. 1 showing both images received in a first bucket and an estimateddisparity between two buckets as depth information;

FIG. 34 is a flowchart showing a method for pixel-wise imaging of ascene, in accordance with an embodiment;

FIG. 35A is an exemplary illustration showing projecting and receiving adirect light path on a scene;

FIG. 35B is an exemplary illustration showing projecting and receivingan indirect light path on the scene of FIG. 35A;

FIG. 35C is an exemplary illustration showing projecting and receiving aspecular light path on the scene of FIG. 35A;

FIG. 35D is an exemplary illustration showing projecting and receivingmultiple different types of light paths on the scene of FIG. 35A;

FIG. 36A is an exemplary illustration of projecting and receiving adirect light path on a scene using the system of FIG. 1;

FIG. 36B is an exemplary illustration of projecting and receivingindirect light paths on the scene of FIG. 36A using the system of FIG.1;

FIG. 37A is an exemplary illustration of projecting and receiving adirect light path on a scene where the light has a lensing effect;

FIG. 37B is an exemplary illustration of projecting and receiving adirect light path on the scene of FIG. 37A compensating for a lensingeffect using the system of FIG. 1;

FIG. 38A is an exemplary illustration of projecting and receivingmultiple light paths on a scene using a complex projection and maskingpattern with the system of FIG. 1; and

FIG. 38B is another exemplary illustration of projecting and receivingmultiple light paths on the scene of FIG. 38A using a complex projectionand masking pattern with the system of FIG. 1.

DETAILED DESCRIPTION

Embodiments will now be described with reference to the figures. Forsimplicity and clarity of illustration, where considered appropriate,reference numerals may be repeated among the Figures to indicatecorresponding or analogous elements. In addition, numerous specificdetails are set forth in order to provide a thorough understanding ofthe embodiments described herein. However, it will be understood bythose of ordinary skill in the art that the embodiments described hereinmay be practiced without these specific details. In other instances,well-known methods, procedures and components have not been described indetail so as not to obscure the embodiments described herein. Also, thedescription is not to be considered as limiting the scope of theembodiments described herein.

Various terms used throughout the present description may be read andunderstood as follows, unless the context indicates otherwise: “or” asused throughout is inclusive, as though written “and/or”; singulararticles and pronouns as used throughout include their plural forms, andvice versa; similarly, gendered pronouns include their counterpartpronouns so that pronouns should not be understood as limiting anythingdescribed herein to use, implementation, performance, etc. by a singlegender; “exemplary” should be understood as “illustrative” or“exemplifying” and not necessarily as “preferred” over otherembodiments. Further definitions for terms may be set out herein; thesemay apply to prior and subsequent instances of those terms, as will beunderstood from a reading of the present description.

Any module, unit, component, server, computer, terminal, engine ordevice exemplified herein that executes instructions may include orotherwise have access to computer readable media such as storage media,computer storage media, or data storage devices (removable and/ornon-removable) such as, for example, magnetic disks, optical disks, ortape. Computer storage media may include volatile and non-volatile,removable and non-removable media implemented in any method ortechnology for storage of information, such as computer readableinstructions, data structures, program modules, or other data. Examplesof computer storage media include RAM, ROM, EEPROM, flash memory orother memory technology, CD-ROM, digital versatile disks (DVD) or otheroptical storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices, or any other medium which canbe used to store the desired information, and which can be accessed byan application, module, or both. Any such computer storage media may bepart of the device or accessible or connectable thereto. Further, unlessthe context clearly indicates otherwise, any processor or controller setout herein may be implemented as a singular processor or as a pluralityof processors. The plurality of processors may be arrayed ordistributed, and any processing function referred to herein may becarried out by one or by a plurality of processors, even though a singleprocessor may be exemplified. Any method, application or module hereindescribed may be implemented using computer readable/executableinstructions that may be stored or otherwise held by such computerreadable media and executed by the one or more processors.

The following relates generally to imaging, and more specifically, to amethod and system for pixel-wise imaging.

“Pixel-wise”, as used herein, generally refers to operations orfunctions on a per-pixel or pixel-by-pixel basis; however, it isunderstood that in some cases, pixel-wise can include operations orfunctions on a small-group-of-pixels by small-group-of-pixels basis.

Embodiments of the present disclosure apply to, at least,intensity-based imaging, visible light or infra-red imaging, spectralimaging, impulse-based and continuous-wave time-of-flight imaging,polarized imaging, structured light imaging, depth sensing or any othertypes of scanning, and two-dimensional and three-dimensional imagingapplications with or without active illumination.

When an image is captured under controlled lighting, the power of thelight source is an important factor: all things being equal, brightersources will generally send more photons to an imaging sensor during anexposure, which can produce a brighter and less noisy image. However,brightness of the light source is just one way to control the quantityof light that reaches the imaging sensor. Some approaches use variousdevices to transport light from a light source to a captured scene, orfrom the scene to the imaging sensor. These devices can be programmable,for example, digital micro-mirror devices, liquid crystal panels, phasemodulators, or the like. In these cases, it is often desirable toprogram a spatio-temporal behavior of these devices to maximize energyefficiency for a given imaging task, power, and/or exposure time. Theseconcerns are especially relevant for live imaging, where short exposuresand low-power restrictions leave little room for wasting light. Theinfluence of signal-to-noise ratio (SNR) on range and acquisition speedcan severely limit practical applications of computational imaging andillumination methods.

Additionally, light propagation through a scene is generally a complexphenomenon; for example, light reflects and refracts, light undergoesdiffuse and specular inter-reflections, light scatters volumetrically,light creates caustics, and the like. Light may do all of the abovebefore reaching an imaging sensor. These transport events, broadlyreferred to as global or indirect light transport, generally dominate,or contribute significantly, to the appearance of objects and scenes inthe world around us because such objects have opaque, refractive ortranslucent aspects. In view of the above complex phenomena of light,conventionally, analyzing global light transport is extremelychallenging. Advantageously, embodiments of the present disclosureprovide pixel-wise programmable-exposure imaging to deal with thesephenomena.

A particular type of camera that can detect direct vs. indirect incominglight, called a transport-aware camera, generally uses a programmablelight source and a programmable sensor mask. Such a camera can be usedfor various applications; for example, 3D sensing, visual recognition,gesture analysis, robotic navigation, industrial inspection,medical/scientific imaging, and the like. Generally, transport-awarecameras require a large mechanically deforming digital micro-mirrordevice (DMD) to implement programmable sensor masking. This approach canhave several disadvantages; for example, excessive form factor,prohibitive distortion due to DMD-imposed large-lens curvature, lowelectro-mechanical mask update speed significantly limiting the range ofapplications, high power dissipation hindering mobile implementations,and high cost.

Embodiments described herein provide a class of optical image sensors(or imagers), image sensing systems, and methods for image sensing thatadvantageously have pixel-wise programmable exposure during one frametime. Unlike other image sensors, where each pixel records approximatelyall incident light during an exposure time, pixel-wise programmableexposure imagers (PPEI) can be programmed to collect and sort theincident light on each individual pixel to one, two or multiple outputsat arbitrary intervals during one frame time.

As an example, as described herein, image sensors of the presentembodiments can be advantageously used for detecting direct andin-direct light in transport-aware imaging techniques. The image sensorsof the present embodiments can also be used for other applications; forexample, intensity-based imaging, visible light or infra-red imaging,spectral imaging, impulse-based and continuous-wave time-of-flightimaging, polarized imaging, structured light imaging, depth sensing,other types of 2D and 3D imaging applications with or without activeillumination, or the like.

In certain embodiments described herein, certain components of lighttransport can be selected, for example, direct-only contributions,indirect-only contributions, specular indirect contributions, or thelike, by dismissing “undesirable” light paths so that they cannotcontribute to an image formed on an imaging sensor. In an embodiment,this can be achieved by synchronously controlling light both at itssource (for example, a projector) and its destination (at the imagingsensor) within one subframe, or frame, time period. To acquire oneimage, a whole sequence of ‘N’ arbitrarily programmable patterns areprojected onto a scene of one or more objects. In an exemplaryembodiment, up to 1000 mask patterns per 30 Hz video frame. During theprojection, the imaging sensor integrates light over ‘N’ “sub-frames”.At the same time, a second sequence of ‘N’ patterns, derived from thefirst patterns and applied in lockstep, controls an arbitrarilyprogrammable pixel mask (as described herein) that, in some cases,prevents light from registering at pixels that are affected by the mask,or in other cases, directs light into another bucket. Thus, in thisexample, an overall imaging behavior, being a set of direct and/orindirect paths, can be determined by a precise sequence of projectorpatterns and sensor masks.

Practical realization of transport-aware imaging generally requirespixel-wise control over precisely which light paths are received, andwhich are blocked, at the imaging sensor. Advantageously, the presentembodiments provide a system and method for performing arbitrarilypixel-wise time-programmable exposure, in for example transport-awareimaging, without the need for mechanical-based devices.

Referring now to FIG. 1, a system 100 for pixel-wise imaging, inaccordance with an embodiment, is shown. As understood by a personskilled in the art, in some cases, some components of the system 100 canbe executed on separate hardware implementations. In other cases, somecomponents of the system 100 can be implemented on one or more generalpurpose processors that may be locally or remotely distributed.

FIG. 1 shows various physical and logical components of an embodiment ofthe system 100. As shown, the system 100 has a number of physical andlogical components, including one or more processors 102, data storage104, an output interface 106, an image sensor 110, a control module 112,a signal storage module 114, a digitization module 116 and a local bus118 enabling the components to communicate each other. In an embodiment,the control module 112 can be executed on the one or more processors. Inother embodiments, the control module 112 can be implemented in hardwareor via a dedicated processor.

The output interface 106 enables another electronic device or computingdevice to transmit data (such as mask data) or receive the outputs fromthe system 100, as described herein. On some embodiments, the outputinterface 106 enables a user interface 106 to view such outputs, via forexample, a display or monitor. In some cases, the outputs from thesystem 100 can also be stored in the data storage 104. In an example,the system 100 can be used for transport-aware imaging, where the imagesensor 110 can use arbitrary pixel masking to select desirable lightpaths. In some cases, this masking can take different shapes and canchange many times during a single image frame exposure.

FIG. 2A shows examples of pixel masking for illustrative purposes for aplurality of in successive sub-frames in a single frame. In a firstexample 302, a rolling masking in illustrated where, in successivesub-frames, only one horizontal line of pixels is registering light;mimicking a traditional rolling shutter apparatus. In a second example304, a rolling band masking is shown where, in successive sub-frames,only a grouping of pixels is registering light; this grouping being lessthan a whole line of pixels. In a third example 306, an arbitrarymasking is applied. “Arbitrary” in this case means registering light atany arrangement or combination of one or more pixels in the imagingsensor 110; such pixels not necessarily neighbouring each other. Thisarrangement can be changed from one subframe to the next.

Accordingly, the system 100 can individually select which pixels are tobe masked. In an embodiment, when a pixel is “masked,” a first signalcollection node in the signal storage module 114, associated with thatpixel, herein referred to as a first “bucket”, does not integrate(collect) a signal from that respective pixel. In some cases, instead, asecond signal collection node (an alternative bucket or second bucket)in the signal storage module 114, associated with that pixel, integratesthe charge from that signal. This allows the system 100 to implementmasking without losing any of the received photons, and thus allows thesystem 100 to be more efficient. In some cases, the “complementary”signal which is collected by the second bucket may be used in variouscomputational imaging applications. Conversely, when a pixel is“exposed” and does not have masking applied, the first bucket collectsthe signal from the respective pixel and the second bucket will notreceive the signal. FIG. 2B shows an exemplary illustration of thisapproach. When a masking bit, associated with a particular pixel, in thecontrol logic module is ‘0’, the photons received at the pixel areintegrated in a second bucket. Conversely, when the masking bit is 1,the photons received at the pixel are integrated in a first bucket. Inthis case, the masking bit can be changed for every sub-frame.

FIG. 3 illustrates an exemplary embodiment of control logic module 112.In order to load, store and apply pixel-wise masks, in-pixel memory canbe used. FIG. 3 depicts an exemplary diagram of one embodiment of apixel where memory needed for sorting the pixel masks is provided orembedded with the pixel. In some cases, logic circuits can also beincluded to control signal “sorting” into one or more buckets based onmask values. The sorting of the signal (electrons) into one or morebuckets for the light received by the pixel in the sensor can beperformed by the control logic module 112, acting as a multi-bucketphotonic mixing device (PMD), by selecting an appropriate bucket basedon the respective mask value. The system 100 can have one or more (‘k’)buckets, and therefore ‘k’ different pixel outputs (readouts) for theoutput interface 106 or data storage 104.

A particular embodiment of the system 100 is one in where there are twobuckets per pixel in the signal storage module 114. In this embodiment,the signal received by each pixel would be separated among two buckets(two storage nodes) associated with that pixel. This arrangement isexemplified in the diagram in FIG. 4. In this example, an arbitrarypattern code is loaded into the control logic module 112, in some casessequentially, prior to each of the pixels being exposed to light. Logicgates in the control logic module 112 can be used to decode a value foreach of the masking bits, and thus provide appropriate control signalsto a pixel readout circuit in the control logic module 112. Thesecontrol signals can be used to control the charge transfer from thepixel photodiode in the imaging sensor 110 to one of two storage nodes(buckets or floating diffusion nodes) in the signal storage module 114.In the example of FIG. 4, if the masking bit signals that the pixelshould be masked, the control logic would provide such control signalsto block the charge (signal) transfer from the photodiode to the firststorage node, and permit the charge (signal) transfer from thephotodiode to the second storage node. In some cases, pixel outputamplifiers in the digitization module 114 can take the signal (in thiscase, voltage) from the corresponding storage node and transfer it (orin other words, buffer it) to a respective pixel readout column line. Asshown in FIG. 4, the memory for storing the mask bits in the controllogic module 112 is split into two separate blocks; a first memory blockfor preloading a next pattern of masking bits and a second memory blockfor applying a current pattern of masking bits. When implementing themask load, storage and usage, it can be useful to keep mask handlingindependent of the pixel exposure in order not to limit the timeavailable for signal collection. Therefore, a pipelined operation ofpre-storage of masking bits can be used via two memory blocks. Thepipelined operation has an intended advantage of applying the masks toall pixels simultaneously (globally).

While the present disclosure references the image sensor 110 as aphotodiode, any suitable photo-detector can be used; for example, apinned-photodiode, a photo-gate, a charge-coupled device, a chargeinjection device, a single photon avalanche diode, or the like. Whilethe present embodiments refer to a visible spectrum of light, light asreferred to herein is understood to include any part of theelectromagnetic spectrum along with, or instead of, light from thevisible spectrum; for example, in the ultraviolet, near-infrared,short-wave infrared, and/or long-wave infrared.

An example of a circuit structure for a pixel using the above exemplarystructure is illustrated in FIG. 5. The first memory cell (latch), inthe first memory block, is used to store the mask bit. The mask bitsignal is routed vertically and is physically the same for the singlecolumn. When a corresponding LOAD ROW trigger signal arrives, the wholerow of masks is loaded at the same time. In some cases, the mask bitscan be loaded serially through separate channels and the bits can thenbe deserialized into a parallel data, i.e. 1-bit per every individualcolumn. Once all the masks are loaded for all the rows individually, thecomplete mask for the full frame is latched by the second latch, in thesecond memory block. An example of this mask loading approach, for asingle subframe, is exemplified in the illustration of FIG. 6. The maskloading approach can then be repeated for every subframe within a singleframe. The two memory blocks allow for masking of light exposure for acurrent subframe, while masking patterns for the next subframe areloaded row-by-row. This results in pipelining the operation of the maskdeserialization and loading with the regular pixel operation. The firstcell is used to load the masks in a sequential “row-by-row” fashion.Once all rows receive their corresponding masks, the masks are thenapplied for the full pixel array simultaneously by loading the secondmemory cell. Depending on the state of the latched mask bit, switchesSW1 and SW2, in the control logic module 112, can be used to steer thecollected charge towards the appropriate bucket in the signal storagemodule 114. In this case, either a first bucket represented by capacitorC_(FD1) or a second bucket represented by capacitor C_(FD2). Moreover,since one of the switches is kept on during the readout, the channelcapacitance of the switch modulates the overall floating diffusioncapacitance. This allows the pixel to intrinsically have a differentconversion gain in two buckets. For the exemplary application of directand indirect light collection, this is an advantageous feature becauseusually direct light has significantly higher power than indirect light.An exemplary implementation of the circuit structure of FIG. 5 is shownusing a transistor arrangement in FIG. 7; where the output ‘Q’ of thesecond latch is connected to ‘C’, the output ‘Q’-bar of the second latchis connected to ‘Cb’, and ‘CD’ is used to flush the charges on thebuckets.

As shown in FIGS. 35A to 35D, light is captured by a conventionalcamera, or other image sensor, independent of the path the light takes.In contrast, an application of the system 100 is to discriminatelycapture light based on the path of the light. An example of a capture ofepipolar direct and indirect light in a single pixel using the system100 is illustrated in FIGS. 36A and 36B respectively. In some cases, aprojector (or light source) can project a sheet of light, or in othercases, project via a raster-scan operation. FIGS. 36A and 36B each showan exemplary subframe out of n subframes. FIG. 36A illustrates capturinga direct light path of a specific pixel. While FIG. 36B illustratescapturing indirect (both scattering and specular) light. By defining aset of pixels (in this case a plane of pixels) at the image sensor 110that correspond to a pattern projected at the projector (in this case acorresponding plane of pixels), the image sensor can collect light in afirst bucket in the signal storage module 114 from light with directpaths and collect light in a second bucket in the signal storage module114 from light with indirect paths. The set of pixels can be defined atthe image sensor 110 using the control logic module 112 which, forexample, applies a mask value of 1 for pixels that correspond to directlight paths and a mask value of 0 for pixels that correspond to indirectlight paths.

In further embodiments, where only the direct light paths or only theindirect light paths are desired, only the light received from thecorresponding pixels is stored in the signal storage module 114 and theother received light is discarded. In this way, in some cases, anoff-the-shelf image sensor 110 can be used under specific lighting andtiming conditions.

In some cases, there may be radial distortion from a lens connected tothe image sensor 110, and in some cases, connected to the projector. Thelens can cause a straight-line path from the projector to map to acurved line path on the image sensor 110, as shown on FIG. 37A. In acase of a rolling shutter image sensor 110, timing conditions can resultin significant loss in ambient or indirect-blocking performance. Usingthe system 100, as shown in FIG. 37B, the mask pattern can be programmedto mask the image sensor 110 in a curved fashion to accommodate thecurved path of the light due to the lens.

FIGS. 38A and 38B illustrate an example of a more complex maskingpattern and projection pattern, including multiple planes (and othershapes) of corresponding pixels. In this case, the projector can projectarbitrary projection patterns, which correspond to pixel maskingpatterns at the image sensor 110. In an example, the projector can be aDLP-based projector. This system 100 collects direct+½ indirect light inone bucket of the signal storage module 114 and ½ indirect light in theother bucket of the signal storage module 114. FIGS. 38A and 38Billustrate an example for one pixel in two different subframes. FIG. 38Ashows a collection of direct+½ indirect in bucket 1 and FIG. 38B shows acollection of ½ indirect in bucket 2. In this case, an image withdirect-path only contributions can be extracted by subtracting the pixelvalues of bucket 2 from that of bucket 1.

It will be appreciated that FIGS. 36A to 38B are illustrationssimplified for the ease of presentation for this disclosure. Inpractical circumstances, the image sensor 110 and the projector can becalibrated such that the mapping of the pixels of the projector to thepixels of image sensor 110 can be determined with the pixel masks andthe projections patterns determined accordingly. In practice, dependingon the circumstances in which they are used, the pixel masks and theprojections patterns do not necessarily have to appear complementary.

In cases where there is a stereo pair (in this case, the image sensorand the projector), a matrix can be used, called a fundamental matrix F,that relates lines of pixels on the image sensor 110 to lines of pixelsprojected by the projector. The fundamental matrix allows the system100, via the processors 102, to determine lines of pixels on theprojector that correspond to lines of pixels on the image sensor 110that represent direct paths of light. For example, if there are x₁ andx₂, which are points on the image sensor 110 and the projectorrespectively, then x₁′ F x₂=0 if and only if x₁ and x₂ are oncorresponding epipolar lines. If x₁ or x₂ are fixed, then x₁′F and Fx₂provide parameters of a corresponding line (ax+by+c=0). In this case,homogeneous coordinates are used for x₁ and x₂, which means that theyare 3D vectors with the first two coordinates being an x and y positionsrespectively on the image sensor/projector, and the last coordinatebeing 1. Accordingly, fundamental matrix F can be used to findcorresponding epipolar lines.

In an example, the fundamental matrix can be determined usingcorrespondences. Since x₁′ F x₂=0, correspondences can be determinedbetween the image sensor 110 and the projector, which provides lists ofcorrespondences (x₁ and x₂). A system of linear equations can be solvedto determine the elements of fundamental matrix F.

In the present embodiments a latch can be used as memory, however infurther embodiments, any suitable data memory storage device may beused; for example, flip-flop, SRAM, DRAM, FLASH, memristor, PCM,magnetic hard-drive, charge bucket, or the like.

Generally, on a physical-level, signal masking (or mixing or sorting)uses an implementation of multiple charge transfer gates, where thegates are used to convey the signal (flow of electrons as a result ofreceived light energy) towards the appropriate bucket. An example ofportions of an integrated circuit layout for the system 100 is shown intop-view in FIG. 8A. This exemplary embodiment uses two buckets(referred to as floating diffusions—FD1 and FD2). Floating diffusion isimplemented as an n-doped region of silicon sitting in a p-dopedsubstrate. TX1 and TX2 are transfer gates to implement the controllogic, the gates are implemented using polycrystalline silicon. Theimage sensor 110 is a pinned-photodiode of PNP-type structure with athin highly doped p-layer (pinning layer) sitting on top of a N-dopedregion implanted on a lightly doped p-substrate (photodiode). Anotherexemplary embodiment is shown in FIG. 8B, which illustrates a pluralityof (k) buckets. Thus, necessitating a greater number of transfer gates(TX1, TX2, . . . TXk) and a greater number of floating diffusion nodes(FD1, FD2 . . . FDk).

Arbitrary pixel-wise programmable exposure can be implemented using anin pixel signal storage nodes in the signal storage module 114 and acombination of transfer gates in the control logic module 112. A crosssection of another exemplary implementation of an integrated circuitlayout for the above is shown in FIG. 10. In this example, a pinneddiode structure is used both as a photodetector and as a signal storagedevice. An integrated circuit layout for the above is shown in FIG. 9and corresponding signal waveforms for its operation are shown in FIG.11. In this example, as shown in FIG. 9, TXg is a global transfer gatein the signal storage module 114 used to transfer the signal (charge)from a pinned photodiode (PPD) in the image sensor 110 to a storagenode, in the signal storage module 114, at the end of each subframe.This transfer is completed at the same time for each pixel in the imagesensor 110 pixel array. The structure of the storage node is similar tothe pinned photodiode (PPD) device, but it is shielded from the incominglight and only used to store charge; thus, it is not used to collectlight-induced electrons like the photo-detecting pinned-photo-diode.Transfer gates TX1 and TX2 in the control logic module 112 are used tocontrol flow of the charge to the buckets; in this case, two bucketsreferred to as floating diffusions FD1 and FD2. The transfer gates arecontrolled based on a value of a masking bit, as described above.Therefore, the voltage of the global transfer gate (TXg) becomes highafter every subframe, as illustrated in the waveform of FIG. 11. Thevoltages of transfer gates TX1 and TX2 go high starting from thebeginning of each subframe in a sequential fashion (for example,row-by-row). Since the storage node for each pixel in the rows of pixelsare read sequentially, depending on the value of the masking bit foreach pixel, a different transfer gate can be set high for each pixel(either TX1 or TX2). Therefore, in this example, a charge stored in thestorage node associated with a previous subframe, can be transferred tothe floating diffusion while the pinned photodiode is integrating(collecting) charge of a current subframe.

In further cases, arbitrary pixel-wise exposure control of system 100can be used and applied in various imaging modalities. FIG. 12illustrates an exemplary layout of portions of the system 100 for use incontinuous-wave time-of-flight imagery. Time-of-flight imaging techniqueinvolves temporal modulation (at the light source) and demodulation (onthe sensor side) of light intensity which allows the processor 102 ofthe system 100 measure distances to objects in the scene, and thereforeto reconstruct a 3D view of the scene. The distances are measured byestimating the phase difference between the transmitted and receivedlight signal intensity. The received light signal has a phase-shiftcompared to the transmitted light due to the time needed for light totravel from the light source to the object, and to travel back to thesensor after being reflected. This allows the system 100 tosimultaneously operate as both a coded-exposure and a time-of-flightsensor to render 3D imaging insensitive to all types of multipath andbackground interferences. This allows the system 100 to improveperformance and enables it to have advantageous capabilities; forexample, time-of-flight imaging, such as “seeing around corners,” orsparse deconvolution by time-encoding. Due to its capability to providea 3D representation of a visual scene, time-of-flight represents anadvantageous application of the system 100.

FIG. 13 illustrates exemplary timing diagram for one pixel showingsignal waveforms to implement time-of-flight pixel masking. When thepixel is masked (represented by a binary code of 1), both oftime-of-flight modulation gates (TX1 and TX2) in the control logicmodule 112 are closed, and therefore no signal is integrated. Draingates (TXD) in the in the control logic module 112 are opened at thattime to drain any residual charge (signal) from the photodetector toavoid any interference between consecutive signal samples. When thepixel is unmasked, also known as exposed (represented by a binary codeof 0), the modulation gates (TX1 and TX2) in the control logic module112 are alternatively opened such that buckets FD1 and FD2 in the signalstorage module 114 collect the signal based on the shape and phase ofthe demodulation signal. In the case of FIG. 13, the first bucket FD1receives the signal when a modulation signal, associated with amodulated light source, is on, and the second bucket FD2 receives thesignal when the modulation signal is off. In this way, a phasedifference between the modulated light source and signal received at theimage sensor can be determined, and thus used to determine time offlight.

FIG. 14 illustrates an exemplary structure of portions of system 100 fora multi-pixel array. This implementation uses a combination of twoin-pixel latches, as described with respect to FIG. 7, to sequentiallyload bit masks row-by-row, then apply the masks globally for a subframeto mask the pixel array approximately simultaneously.

Another example of a CMOS image sensor implementation of portions of thesystem 100 is shown in FIG. 15. As shown, there is a typical arrangementof peripheral circuits and interfaces for an imaging sensor. An exampleof a timing diagram showing signal waveforms of masking data for thisexemplary implementation are shown in FIG. 6.

Another exemplary structure of portions of the system 100 is shown inFIG. 16. In this case, peripheral circuits and interfaces for theimaging sensor are split between the top and bottom sides of the pixelarray.

FIG. 17 illustrates another example of the arbitrary pixel-wiseprogrammable exposure of parts of the system 100 as applied to a linesensor type of imaging sensor 110. Line sensors can capture photons viaone single pixel row, or via multiple rows of different pixels. In somecases, mask loading circuits of the control logic module 112 may beconnected adjacent each of the pixels. In other cases, the mask loadingcircuits can be located peripherally to the pixel line/array area. Inthe diagrammatic example shown in FIG. 17, the mask loading and signalmodulation circuits are located on one side of the pixel array and thereadout circuits on the other side. Other ways to arrange thesecircuits, including both on-chip and off-chip, are also possible.

FIG. 18 is an exemplary implementation of the system 100 in a cameraenvironment. In this case, the per-pixel programmable exposure imagesensor 110 is denoted as imager integrated circuit (IC). The cameraenvironment includes data storage 104, depicted here by anoff-imager-chip DRAM memory (DDR), with masking controls stored in DRAMand sent to Imager IC by an FPGA. The code-storing memory can also beimplemented directly on the imager IC or another IC wire-bonded,flip-chip bonded or chip-stacked with it. The digitization module 116(here denoted as analog-to-digital converter (ADC)) converts the signalfrom analog charges to digital values, and in some cases, may be locatedoff-chip. In other cases, the ADC can also be implementedon-imager-chip.

The embodiments described herein can provide image sensing systems thatcombine spatial and temporal exposure coding to deliver per pixelprogrammability and thus enhanced performance capabilities to imagingapplications. As exemplified by testing done by the Applicant, thenumber of arbitrary pattern-mask exposures within one video framecapable by the system 100 can reach and exceed 1000 for a nominal framerate of 30 frames-per-second. This is a substantial increase of over anorder of magnitude in the amount of processed sensory informationcompared to any approaches that use digital micro-mirror devices, liquidcrystal panels, phase modulators, or the like.

Additionally, cameras utilizing the embodiments described herein can beadvantageously used in applications in which refraction and scatteringcan be selectively blocked or enhanced. For example, allowing visualstructures too subtle to notice with the naked eye can become apparent.In another example, object surfaces can be reconstructed in threedimensions using time of flight approaches under challenging conditions,such as under direct sunlight, beyond of what is possible withconventional imaging technologies. Thus, “depth cameras” using thepresent embodiments can have had a tremendous impact on computer visionand robotics technologies.

Using the embodiments described herein, transport-aware imagers can beprogrammed to selectively detect only some of that light, depending onthe actual 3D paths the light beams followed through a scene.Application domains of such imagers are numerous; for example, 3Dsensing, visual recognition, gesture analysis, robotic navigation,industrial inspection, and medical/scientific imaging. Conventionaltransport-aware camera prototypes typically require a large mechanicallydeforming digital micromirror device (DMD) to implement programmablesensor masking, which introduces a number of significant disadvantages;for example, they have an excessively large form factor that is abarrier to portable consumer electronics, they have prohibitively highlevels of distortion due to DMD-imposed large-lens curvature, they havelow electro-mechanical mask update speeds that significantly limit therange of applications, they have high power dissipation that hindersmobile implementations, and they have a prohibitively high cost. Incontrast, the embodiments described herein offer previously unattainableversatility in coded-exposure imaging (CEI).

In experiments, using a low-power projector, the system 100 hasdemonstrated several generally unique capabilities. For example,reconstructing 3D objects in challenging visual scene conditions. FIG.27 shows a captured 3D map of a 1600 Lumen light bulb with aconventional camera (above) and with the system 100 (below). FIG. 28shows an image in bright sunlight with a conventional camera (above) and3D imaging using the system 100 (below) in bright sunlight. FIG. 29Ashows capturing only direct light reflected only once in a scene usingthe system 100. FIG. 29B shows that same scene except this time showingonly capturing indirect light, which is the light reflected multipletimes in the scene, using the system 100. FIG. 30A shows the system 100being used to capture only indirect light and thus being able to, atleast partially, see through a latex glove; or as shown in FIG. 30B, atleast partially, see through skin of a human hand. FIG. 31A shows ascene of ice blocks captured by a conventional camera. FIG. 31C shows 3Dimaging of the ice blocks, using the system 100, by sensing the time ofdirect-only light travel. In contrast to FIG. 31B which shows a 3D imagecaptured using conventional time-of-flight imaging where indirect light(bouncing off multiple objects before returning to the camera) skews theresulting image and reduces depth resolution.

Time-of-flight cameras, as described herein, can be used for vision andcomputational photography tasks, for event cameras that supportasynchronous imaging for high-speed motion analysis, and for 3Dscanning. Using the system 100 described herein, a coded two-bucket(C2B) camera can be implemented for, at least, time-of-flight imaging.The C2B camera is a coded exposure camera that generally does not blockincident light. Instead, it modulates the incident light arriving ateach pixel by controlling which of the two “buckets” in the signalstorage module 114 associated with the pixel should integrate it. Inthis way, the system 100 can output two images per video frame, one perbucket, and allows rapid, fully-programmable per-pixel control of theactive bucket via binary 2D masking patterns.

The light efficiency and electronic modulation of C2B cameras makes themparticularly well suited for coded-exposure imaging and light transportanalysis tasks. An exemplary application of the system 100, as describedbelow, is for dense one-shot three-dimensional (3D) reconstruction.Specifically, using one C2B video frame of a dynamic scene under activeillumination, reconstructing the scene's 3D snapshot, via per-pixeldisparity or normals, at a resolution as close as possible to theimaging sensor's pixel array. The Applicant advantageously determinedthat C2B cameras, using approaches described herein, allows for solvingof a very technically difficult 3D reconstruction problem by exploitinga two-dimensional (2D) problem of image demosaicing. FIG. 32 illustratesan example of images captured using the system 100 showing both imagesreceived in the first bucket and determined normal. FIG. 33 illustratesan example of images captured using the system 100 showing both imagesreceived in the first bucket and estimated disparity between the bucketsas depth information.

As shown, C2B cameras can acquire, in one video frame, views of a sceneunder L linearly-independent illuminations, multiplexed across bucketsof L−1 pixels. Such a frame is referred to as a two-bucket illuminationmosaic. For this mosaic, the ratio of bucket measurements at each pixelis an illumination ratio, which is less dependent on spatial albedoand/or reflectance variations, and is potentially easier to demosaic.Additionally, by demosaicing either the illumination mosaic or itsbucket ratio, full-resolution images of an imaged scene can be obtainedfor the purpose of dense reconstruction.

Generally, conventional coded-exposure sensors cannot control per-pixelexposure because they rely on a global signal to set the active bucketof all pixels. In this respect, the C2B camera, using system 100, allowsfor an optimal tradeoff between the desire for multiple measurements perpixel, which leads to large pixels, complex designs and small fillfactors, and the desire to maintain flexibility by not hard-coding onthe imaging sensor the number of simultaneous per-pixel measurements.

In an embodiment, pixels in a C2B camera, incorporating system 100,differ from those of a conventional camera. In a C2B camera, each pixelis associated with two buckets in the signal storage module 114. Eachbucket can be a distinct circuit, in some cases an analog circuit, forintegrating light received at the photodetector 110 of the pixel. Bothbuckets can integrate the light that falls onto the pixel'sphoto-sensitive area but, in most cases, only one them is activelyintegrating at any given time. As above, each pixel has associated withit a one-bit digital memory (known as a mask) in the control logicmodule 112 that controls which of its two buckets is active, asdiagrammatically illustrated in FIG. 19. This mask is programmable, itcan be updated many times within a single frame (as shown in the timingdiagram of FIG. 20), and each pixel's associated mask may differ frompixel-to-pixel. At the end of each frame, two intensities can be readout and digitized by the digitization module 116 for each pixel, i.e.,the digitized contents of the pixel's two buckets. In the presentembodiment, C2B cameras can therefore output two images per video frame,one for each bucket; referred to herein as a bucket-1 image and abucket-0 image, respectively.

Programming of a C2B camera can include specifying time-varying contentsof each pixel's associated masking value at various timescales; forexample, (1) at the scale of sub-frames within a video frame, whichcorresponds to updates of in-pixel memories, or (2) at the scale offrames within a video sequence. For a video sequence with F frames and acamera that has P pixels and supports S sub-frames, bucket activitiescan be represented as a three-dimensional binary matrix C of size P×F×S.C is referred to as a code matrix and is diagrammatically illustrated inFIG. 21.

As illustrated in in FIG. 21, two specific 2D “slices” of the codematrix C can be used. For a specific pixel p, slice C^(p) describes theactivity of pixel p's buckets across all frames and sub-frames.Similarly, for a specific frame f, slice C_(t) describes the bucketactivity of all pixels across all sub-frames of f:

$c^{p} = \underset{\underset{f \times s}{︸}}{\begin{bmatrix}c_{1}^{p} \\c_{2}^{p} \\\vdots \\c_{F}^{p}\end{bmatrix}}$${c_{f} = \underset{\underset{p \times s}{︸}}{\begin{bmatrix}c_{f\; 1} & c_{f\; 2} & \cdots & c_{fS}\end{bmatrix}}},$where c^(p) is an S-dimensional row vector that specifies the activebucket of pixel p in the sub-frames of frame f; and c_(fs) is a columnvector that specifies the active bucket of all pixels in sub-frame s offrame f.

Although C2B cameras can be used for passive imaging applications inplace of coded-exposure cameras, the present embodiment considers themore general case where illumination is programmable at sub-frametimescales. In particular, the scene's time-varying illuminationconditions are represented as an S×L illumination matrix L that appliesto all frames:

${L = \underset{\underset{s \times l}{︸}}{\begin{bmatrix}l_{1} \\\begin{matrix}l_{2} \\\begin{matrix}\vdots \\l_{S}\end{matrix}\end{matrix}\end{bmatrix}}},$where row vector I_(s) denotes the scene's illumination condition insub-frame s of every frame. In this example, two types of sceneillumination are considered: a set of L directional light sources whoseintensity is given by vector I_(s); and a projector that projects apattern specified by the first L−1 elements of I_(s) in the presence ofambient light, which is treated as an L-th source that is “always on”(i.e., element I_(s)[L]=1 for all s).

For two-bucket image formation model for pixel p, let i^(p) and î^(p) becolumn vectors holding the intensity of bucket 1 and bucket 0 associatedwith pixel p, respectively, in F frames. This intensity is modelled asthe result of light transport from the L light sources to the twobuckets associated with the pixel; as diagrammatically illustrated inFIG. 22.

$\underset{\underset{2f \times 1}{︸}}{\begin{bmatrix}i^{p} \\{\hat{i}}^{p}\end{bmatrix}} = {\underset{\underset{2f \times s}{︸}}{\begin{bmatrix}C^{p} \\{\overset{\_}{C}}^{p}\end{bmatrix}}\underset{\underset{s \times l}{︸}}{l}\underset{\underset{l \times 1}{︸}}{t^{p}}}$where b denotes the binary complement of matrix or vector b, C^(p) isthe slice of the code matrix corresponding to p, and t^(p) is thepixel's transport vector. Element t^(p)[l] of this vector specifies thefraction of light source l's intensity that is transported to pixel p inthe timespan of one sub-frame, across all light paths and across bothbuckets.

To gain some intuition about the above equation, consider the buckets'intensity in frame f:

${i^{p}\lbrack f\rbrack} = {\underset{\underset{\underset{{{of}\mspace{14mu}{pixel}\mspace{14mu} p},{{bucket}\mspace{14mu} 1},{{frame}\mspace{14mu} f}}{{illumination}\mspace{14mu}{condition}}}{︸}}{\left( {c_{f}^{p}l} \right)}t^{p}}$${{\hat{i}}^{p}\lbrack f\rbrack} = {\underset{\underset{\underset{{{of}\mspace{14mu}{pixel}\mspace{14mu} p},{{bucket}\mspace{14mu} 0},{{frame}\mspace{14mu} f}}{{illumination}\mspace{14mu}{condition}}}{︸}}{\left( {{\overset{\_}{c}}_{f}^{p}l} \right)}t^{p}}$

In effect, the two buckets associated with pixel p can be thought of as“viewing” the scene under two potentially different illuminationconditions given by the vectors c^(p)L and c ^(p)L, respectively.Moreover, if c^(p) _(f) varies from frame to frame these illuminationconditions will vary as well.

For the bucket-1 and bucket-0 image sequences, collecting the twobuckets' intensities across all frames and pixels, two F×P matrices aredefined that hold this data:I=[i ¹ i ² . . . i ^(p)] Î=[î ¹ î ² . . . î ^(p)]

The sequences I and Î can be used as input to recover per-pixel geometry(depth, normals, or both) from multiple intensity measurements at eachpixel.

Using the embodiments described herein, solutions to the technicalproblem of normal and depth estimation using photometric stereo andstructured light stereo can be implemented. As described below, thesetasks are implemented using determinations that are advantageously doneindependently at each pixel, and the relation between observations andunknowns is generally expressed as a system of linear equations. Thedeterminations described herein are merely examples that illustratespecial characteristics of two-bucket imaging; however, using advancedapproaches to handle more general settings is also possible.

For two-bucket constraints from a single frame, shape constraints areprovided by a pixel's associated two buckets. For notational simplicity,the pixel and frame indices are dropped, and instead, the intensity ofeach bucket is denoted with scalars i and î, respectively, and theillumination condition of each bucket is denoted with vectors I=c^(p)_(f)L and Î=c ^(p) _(f)L, respectively.

The relation between intensity and the pixel's unknowns can take thesame form in both photometric stereo and structured light triangulationwith cosine patterns, via the following relationship equations:i=aIDx+e î=aÎDx+êwhere I, Î, D are all known. D is representative of lighting conditions,x is a 3D vector that contains the pixel-specific unknowns; a is anunknown scalar; and e, ê are observation noise. See the TABLE 1 belowfor a summary of the assumptions pertaining to each problem and for themapping of each problem's quantities to the factors in the aboverelationship equations.

TABLE 1 Lambertian photometric stereo Structured-light triangulationw/cosine patterns Assumptions Lambertian reflectance, non-uniformreflectance has non-negligible diffuse component; albedo; calibratedlight sources; robustness to indirect light depends on no ambient orindirect light frequency choice Illumination each l_(l) corresponds toillumination l_(l)[k] = cos(θ_(l) + kϕ_(l)), where (θ_(l),ϕ_(l) givenvectors: l_(l) with only source l turned on, i.e., by the frequency andphase shift of l-th projection element l_(l)[k] non-zero iff l = kpattern Transport t = aDn, where n is the 3 × 1 unit t = aD[s′ b]′, iswhere a is a reflectance factor, b is vector t surface normal and a isthe the contribution of ambient light, and binary vector s Lambertianalbedo indicates the matching projector pixel, i.e., s[k] = 1 iff thatpixel is k (see FIG. 5b) Matrix D row l of D is a 3D vector that row lof D is the vector [cos(θ_(l))-sin(θ_(l))1] represents the unitorientation and intensity of the 1-th light source Vector x x = n x =[cos(kϕ_(l)) sin (kϕ_(l))b]′ if same cosine frequency used for allpatterns; additional frequencies contribute two unknowns each

There are at least three ways to turn the above relationship equationsinto a constraint on normals and depths, under the assumption ofzero-mean normally-distributed noise.

In a first way, using a direct approach, the above relationshipequations are treated as two independent constraints on vector ax, thensolving for both a and x once enough constraints are available. Theadvantage of this approach is that errors are normally distributed byconstruction. A disadvantage may be that the above relationshipequations depend on albedo (or reflectance). The above relationshipequations may also make single-frame shape estimation harder when avaries from pixel to pixel.

In a second way, using a bucket-ratio (BR) constraint approach, sincethe two buckets represent different illumination conditions, their ratiocan be an illumination ratio. This yields a constraint over x:rÎDx=IDx, where r=î/i.

The bucket ratio r is well approximated by a Gaussian random variablewhose mean is the ideal (noiseless) bucket ratio and its standarddeviation depends weakly on a. Specifically, under typicalsignal-to-noise ratio conditions, i's standard deviation is equal toσ/i_(n), where i_(n) is the noiseless bucket-1 intensity and σ is thestandard deviation of noise. In effect, two-bucket imaging provides one“reflectance-invariant” image per frame.

In a third way, using a bucket cross-product (BCP) constraint approach,instead of computing an explicit ratio from the above relationshipequation, a can be eliminated to obtain:iÎDx={circumflex over (i)}IDxSince the above equation has intensities i, î as factors, it implicitlydepends on albedo.

In the first way, at least three independent DM constraints are requiredto solve for the 3D vector ax. This solving can be accomplished bysingular-value decomposition. In the second and third way, given atleast two independent bucket-ratio (BR) or bucket cross-product (BCP)constraints, x can be determined by solving the generalized eigenvalueproblem they form.

The above approaches provide ways to solve for 3D shape when there areenough independent constraints per pixel. In the following, there isprovided a solution to the problem of capturing a sequence of framesthat provides constraints for a pixel p. In particular, selecting (1)the number of frames F, (2) the number of sub-frames per frame S, and(3) the pixel-specific slice of the F×S code matrix, C^(p). Determiningthese parameters can be thought of as an instance of an optimalmultiplexing problem. This problem deals with one-to-one mapping from Fdesired measurements to F actual, noisy observations. In the case ofcoded two-bucket imaging, the problem is unique because each frameyields two measurements instead of just one.

As a starting point, we expand:

$\begin{bmatrix}i^{p} \\{\hat{i}}^{p}\end{bmatrix} = {\begin{bmatrix}C^{p} \\{\overset{\_}{C}}^{p}\end{bmatrix}{Lt}^{p}}$to get a relation that involves only intensities:

$\underset{\underset{({2F \times 1})}{{bucket}\mspace{14mu}{measurements}}}{\underset{︸}{\begin{bmatrix}i^{p} \\{\hat{i}}^{p}\end{bmatrix}}} = {{\begin{bmatrix}C^{p} \\{\overset{\_}{C}}^{p}\end{bmatrix}\begin{bmatrix}{l_{1}t^{p}} \\\begin{matrix}\vdots \\{l_{S}t^{p}}\end{matrix}\end{bmatrix}}\overset{def}{=}{\underset{\underset{\underset{({2F \times S})}{{matrix}\mspace{14mu} W}}{{bucket}\text{-}{multiplexing}}}{\underset{︸}{\begin{bmatrix}C^{p} \\{\overset{\_}{C}}^{p}\end{bmatrix}}}\mspace{20mu}\underset{\underset{\underset{({S \times 1})}{{{illuminations}\mspace{14mu} l_{1}},\ldots,l_{S}}}{{pixel}\mspace{14mu}{intensity}\mspace{14mu}{under}}}{\underset{︸}{\begin{bmatrix}i_{1}^{p} \\\begin{matrix}\vdots \\i_{L}^{p}\end{matrix}\end{bmatrix}}}}}$

Each scalar i_(s) ^(p) in the above equation is an intensity that aconventional camera pixel would have if the scene's illuminationcondition was l_(s). The above equation indicates that, as far as asingle pixel p is concerned, coded two-bucket imaging multiplexes Sdesired intensity measurements into the pixel's two buckets across Fframes.

With this approach, even though a pixel's two buckets provide 2Fmeasurements in total, generally at most F+1 of them can be independentbecause the multiplexing matrix W is rank-deficient:rank W=min(F+1,S).

As a note, the C2B camera is generally not equivalent to twocoded-exposure cameras that operate completely independently from eachother. This is because the masking that controls bucket activity iscomplementary, and thus not independent. It follows that out of the 2Fintensities captured by a pixel's buckets across F frames, F+1 of themprovide independent constraints and the rest generally provide redundantmeasurements; thus, they are useful for improving performance in thepresence of noise.

For finding the optimal F×(F+1) matrix C^(p). the equation below is usedto obtain a lower bound on a mean-squared error (MSE) of bucketmultiplexing:

${MSE} = {{\frac{\sigma^{2}}{S}{\text{trace}\left\lbrack \left( {W^{\prime}W} \right)^{- 1} \right\rbrack}} \geq {2\sigma^{2}\frac{F^{2} + 1}{{F\left( {F + 1} \right)}^{2}}}}$where for every multiplexing matrix W, the MSE of the best unbiasedlinear estimator satisfies the lower bound of the above equation.

Although the above generally does not provide an explicit construction,it does ensure the optimality of matrices W whose MSE is the lowerbound. This observation can be used to verify that matrices are optimalfor “realistic” values of F. Let C^(p)=¹ (H+1) where H is derived fromthe (F+1)×(F+1) Hadamard matrix by removing its row of ones to create anF×(F+1) matrix. The bucket-multiplexing matrix W defined by C^(p) isoptimal for F≤10000 when (F+1), (F+1)/12, or (F+1)/20 is a power of two.The shortest sequences for which the above applies are F=3 and F=7.Since a primary goal is one-shot acquisition, optimal matrices for othersmall values of F are also of interest. To find them, a brute-forcesearch over the space of small F×(F+1) binary matrices can be used tofind the ones with the lowest MSE. These matrices are shown in TABLE 2below.

TABLE 2 # Frames F = 2 F = 3 F = 4 F = 5 F = 6 MSE Eq. 1.25 1.666661.41667 1.73333 1.54167 bound for σ = 1 Optimal 2.5 1.66666 1.88889 3.42.27778 MSE for σ = 1 Optimal 1 0 0 1 1 0 0 1 1 0 0 0 1 1 0 1 0 0 1 1 10 0 0 0 C^(p) 0 1 0 1 0 1 0 1 0 1 0 0 1 1 0 0 1 0 1 0 0 0 1 1 0 1 0 0 11 0 0 1 0 1 0 1 0 1 0 1 0 0 0 0 1 1 1 0 0 0 1 1 0 1 0 0 1 0 1 1 0 0 1 01 0 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1

A technical advantage of C2B cameras, using system 100, is that they canoffer an alternative to multi-frame acquisition: instead of capturingmany frames in sequence, they can capture a spatially multiplexedversion of them in a single frame. Such a frame is referred to as atwo-bucket illumination mosaic; an analogy to RGB filter mosaics ofconventional color sensors.

Similar to an RGB mosaic, full image sequences I and Î are sampled at1/F of the image sensor's 110 resolution. To compute a 3D shape at fullresolution, the illumination mosaic can be upsampled using imagedemosaicing techniques and then the techniques described herein can beapplied to every pixel independently. Unlike color filter mosaics, whichare attached to color sensors and generally cannot be changed,acquisition of illumination mosaics in the present embodiments is fullyprogrammable for any F. In a particular case, to maximize shaperesolution, acquisition of the densest possible mosaics is considered;those that multiplex F=3 or F=2 frames into one shot. This isillustrated in FIG. 23. Frames in the first three columns were capturedusing a three-frame code matrix C. This matrix assigned illuminationconditions that where the same for all pixels in a frame but differentacross frames. The fourth column shows an illumination mosaic, capturedin one shot, that multiplexes the frames on the left using a 3-pixeltile on the rightmost images.

Acquiring an illumination mosaic amounts to specifying a one-frame codematrix {tilde over (C)} that spatially multiplexes the corresponding Fframe matrix C. This is accomplished by (1) defining a regular F-pixeltiling of the sensor plane and (2) specifying a one-to-onecorrespondence (p_(i), f_(i)), 1≤i≤F, between pixels in a tile andframes. The columns of {tilde over (C)} are then defined to be:

${\overset{\sim}{C}}_{1}^{p_{i}}\overset{def}{=}C_{f_{i}}^{p_{i}}$

In a particular case, there are three different ways of applying theshape estimation approaches described above to the 2P intensities of anillumination mosaic.

In a first way, using intensity demosaicing (ID), an intensity of eachbucket of each pixel in a tile is treated as a separate “color channel”for the purposes of demosaicing. These intensities are upsampled byapplying an RGB demosaicing approach to three of these 2F channels at atime. Then applying any of the shape estimation approaches describedabove to the result.

In a second way, using bucket-ratio demosaicing (BRD), also calledcollection node-ratio demosaicing, a bucket ratio at each pixel isdetermined to turn intensity measurements intoalbedo/reflectance-invariant measurements. The ratio of each pixel in atile is treated as a separate “color channel” for the purpose ofdemosaicing. The shape is determined using the bucket-ratio constraintof:rÎDx=IDx, where r=î/i

In a third way, using no demosaicing (ND), instead of upsampling, eachtile is treated as a “super-pixel” whose shape unknowns (such as,normal, albedo, disparity, and the like) do not vary from pixel topixel. One shape estimate per tile is determined using any of theapproaches described herein. Unlike the other two ways, which yieldper-pixel shape estimates, this way returns 1/F fewer estimates.

The Applicant evaluated the performance of the C2B camera describedherein on synthetic data. The effective resolution and albedo invarianceof normals computed from photometric stereo was determined by (1)applying them to synthetically-generated scenes with spatially varyingnormals and albedo, and noisy images, and (2) evaluating reconstructionperformance against their spatial frequency content. Since alldeterminations, except demosaicing, are done per pixel, anyfrequency-dependent variations in performance are due to these steps.FIG. 24A is a chart that compares several combinations of the approachesdescribed herein. They are also compared against a baseline 3-framemethod that processes full-resolution images, and a color photometricstereo approach. As determined, the C2B camera's data has betterperformance than the color-based photometric stereo approach. FIG. 24Bis a chart that considers the effect of spatial albedo variations. Bothcomparisons in FIGS. 24A and 24B match intuition; i.e., that performancedoes degrade for very high albedo frequencies regardless of the type ofneighborhood processing. Generally, for peak signal-to-noise ratio(PSNR) of at least 30, the C2B cameras confer a substantial performanceadvantage for scenes with spatial frequencies up to one-third theNyquist limit.

In the Applicant's exemplary experiments, the experimental setupconsisted of a C2B camera, a Texas Instruments LightCrafter DMDprojector and 4 LEDs. The camera was able to operate at 16-20 FPS withup to 4 subframes per frame. This allows the running of PhotometricStereo and capturing the data at near video speeds.

To perform ground-truth acquisition, a static scene was createdconsisting of a hat which had colourful bands and textures as well as ofa book which occludes part of the hat, shown in FIG. 26. This scene waschosen because traditionally, one-shot methods have relied on color cuesto infer the appearance of the scene under different lightingconditions. This allows the evaluation of how well shape estimationworks under challenging conditions. The objects were placed 2 m awayfrom the camera. A 23 mm lens was mounted on the camera, providing afield of view of about 30 cm by 30 cm. In both cases, 1000 images werecaptured for each illumination condition to reduce the noise. The groundtruth data was compared to BRD-BR, ID-DM, and ID-DM with one bucket.

For real objects using structured light, ground truth disparityestimation was captured by illuminating the object with 4 phase-shiftedsinusoidal patterns of frequency 1 and 3 phase-shifted quantizedsinusoidal patterns of frequency 16. The projector was placed 60 cm awayfrom the object with a baseline of 1.5 m. The low frequency informationwas used to perform phase unwrapping and the higher frequency quantizedsinusoids as ground truth. Three patterns were used for the single shotacquisition. The results are visualized in FIG. 25A, where forstructured light, BRD-BR yielded the best response with an RMSE of 2.7after outliers are removed. Since all the outliers cannot be removed, anRMSE of 4.7 was reported when the outliers were kept. Since theprojector has 608 columns and a frequency of 16 was used, the maximumerror possible is 608/16=38. Hence, there was an accuracy of about 5-10%of maximum error. Since quantized sinusoids were used, this valueprovides a lower bound on the performance of the C2B camera.

For real objects using photometric stereo, a direction of each lightsource was calibrated using a chrome sphere placed 2 m from the cameraand lights being 2-3 m from the scene. An image was captured using 4subframes, one for each light source, to capture the sequence. Theresults are also visualized in FIG. 25B, and ID-DM was found to performthe best for photometric stereo with an RMS angular error of 10.695° anda median angular error of 5.63°. However, the RMSE for ND-DM is stillquite high over 10°. This may be explained by the non-uniform gain thatis applied to each mask. This means that in the least squaresoptimization B=AX, a skew to A is being applied.

The results support the fact that 3D measurements can be advantageouslyobtained using C2B cameras at, or close to, sensor resolution.

FIG. 34 illustrates a method 300 for pixel-wise imaging of a scene, inaccordance with an embodiment. At block 302, the control logic module112 receives a pixel-wise pattern, the pixel-wise pattern comprising amasking value for each pixel in an array of pixels of the image sensor110. At block 304, each pixel of the image sensor 110 producing anelectronic signal when such pixel is exposed to light received from thescene. At block 306, the control logic module 112 directs the electronicsignal at each pixel to a one or more collection nodes in the signalstorage module 114, associated with such pixel, based on the respectivemasking value. The one or more collection nodes each capable ofintegrating the received electronic signal. In some cases, as describedherein, only one, or some, of the collection nodes receive the signal.

In some cases, at block 308, the digitization module 116 can digitizeand output a measure of the integration at each collection node.

In some cases, at block 310, a processor 102 can make furtherdeterminations based on the integrated values at each of the collectionnodes; for example, a time-of-flight determination, a determination oflight path type (direct, indirect, or specular), depth, normals, or thelike.

Although the invention has been described with reference to certainspecific embodiments, various modifications thereof will be apparent tothose skilled in the art without departing from the spirit and scope ofthe invention as outlined in the claims appended hereto. The entiredisclosures of all references recited above are incorporated herein byreference.

The invention claimed is:
 1. A system for imaging of a scene, the systemcomprising: an image sensor comprising an array of pixels, each pixelcomprising a photosensitive receptor that produces an electronic signalwhen exposed to light received from the scene; a signal storage modulecomprising one or more collection nodes, each collection node capable ofintegrating the electronic signal received by it; and a control logicmodule for receiving a pattern and directing the electronic signal toone or more of the respective collection nodes based on the pattern,wherein the pattern is received for every subframe, and the electronicsignal is directed based on the pattern, each frame comprising aplurality of subframes.
 2. The system of claim 1, wherein the controllogic module comprises a first memory unit and a second memory unit, thesecond memory unit storing the pattern for a current subframe and thefirst memory unit storing the pattern for an upcoming subframe, whereinthe pattern for the upcoming subframe is loaded into the first memorysequentially, and the pattern for the current subframe is stored in thesecond memory for pipelined operation.
 3. The system of claim 1, whereinthe light received from the scene comprises temporally modulated lightfrom a light source and the one or more collection nodes comprisesexactly two collection nodes for each pixel, the system furthercomprising a processor to determine time-of-flight of the modulatedlight by measuring phase differences between the modulated light at thelight source and the light received at the photosensitive receptor, theelectronic signal directed to one of the collection nodes during a firstportion of the modulation of the modulated light and the electronicsignal directed to the other collection node during a second portion ofthe modulation of the modulated light, wherein for each subframe thepattern is used to determine whether the signal is to be demodulated bymeans of the said demodulation process or the signal is to be discarded.4. The system of claim 1, the system further comprising one or morelight sources to project a light-pattern onto the scene, and the patternreceived by the control logic module directs the electronic signal toone of the collection nodes if the light received at the respectivepixel approximately corresponds to one of more of predetermined lightpath types associated with that node, wherein the predetermined lightpath type comprises one of a direct light path, an indirect light path,and a specular light path.
 5. The system of claim 1, wherein the lightreceived from the scene comprises photometric stereo light illuminationconditions from one or more light sources, and the electronic signal isdirected by the pattern to one of the collection nodes for eachrespective illumination condition, the system further comprising aprocessor to determine surface orientations of one or more objects inthe scene based on the intensity of light received.
 6. The system ofclaim 1, wherein the light received from the scene comprises structuredlight illumination conditions, and the electronic signal is directed bythe pattern to one of the collection nodes for each respectiveillumination condition, the system further comprising a processor todetermine the depth to one or more objects in the scene from theintensity of light received via triangulation with pixels at the lightsource and pixels at the image sensor.
 7. The system of claim 1, whereinthe one or more collection nodes are associated with a group of one ormore pixels.
 8. The system of claim 1, wherein the pattern prevents asubset of the array of pixels from registering light received from thescene by directing the control logic module to discard the electronicsignal.
 9. The system of claim 1, wherein the one or more collectionnodes comprises, for each pixel, a first type of collection node and asecond type of collection node, and wherein the pattern directs theelectronic signals received from a first subset of the array ofphotosensitive receptors to a subset of the first type of collectionnodes, and from a second subset of the array of photosensitive receptorsto a subset of the second type of collection nodes.
 10. The system ofclaim 1, wherein the one or more collection nodes comprises, for eachpixel, a first type of collection node, a second type of collectionnode, a third type of collection node, and a fourth type of collectionnode, and wherein the pattern directs the electronic signals receivedfrom a first subset of the array of photosensitive receptors to a subsetof the first type of collection nodes, from a second subset of the arrayof photosensitive receptors to a subset of the second type of collectionnodes, from a third subset of the array of photosensitive receptors to asubset of the third type of collection nodes, and from a fourth subsetof the array of photosensitive receptors to a subset of the fourth typeof collection nodes.
 11. The system of claim 10, wherein the lightreceived from the scene comprises temporally modulated light from alight source, wherein the first type of collection node and the secondtype of collection node comprise a first pair of collection nodes andthe third type of collection node and the fourth type of collection nodecomprise a second pair of collection nodes, the system furthercomprising a processor to determine time-of-flight of the modulatedlight by measuring phase differences between the modulated light at thelight source and the light received at the photosensitive receptor, theelectronic signal directed to one of the collection nodes in either thefirst pair or the second pair during a first portion of the modulationof the modulated light and the electronic signal directed to the othercollection node in the same pair during a second portion of themodulation of the modulated light, wherein for each subframe the patterndirects whether the signal is demodulated in the either the first pairof collection nodes or the second pair of collection nodes, and wherethe collection nodes in the other pair of collection nodes act as twoadditional signal collection nodes.
 12. The system of claim 1, whereinthe control logic module comprises an electronic signal storage node tostore the electronic signal generated by the photosensitive receptorduring exposure of a given subframe, and wherein, subsequently, theelectronic signal stored in the electronic signal storage node isdirected to one or more of the respective collection nodes based on thepattern.
 13. The system of claim 1, wherein the control logic modulefurther comprises a memory unit to load and store the pattern.
 14. Amethod for imaging of a scene, the method comprising: receiving apattern; receiving electronic signals from an array of photosensitivereceptors when such photosensitive receptors are exposed to lightreceived from the scene; and directing the electronic signals to one ormore collection nodes based on the pattern, wherein the pattern isreceived for every subframe, and the electronic signals are directedbased on the pattern, each frame comprising a plurality of subframes.15. The method of claim 14, wherein the light received from the scenecomprises temporally modulated light and the one or more collectionnodes comprises exactly two collection nodes for each pixel, the methodfurther comprising determining time-of-flight of the modulated light bymeasuring phase differences between the modulated light at the lightsource and the received light, and wherein directing the electronicsignal comprises directing the electronic signal to one of thecollection nodes during a first portion of the modulation of themodulated light and directing the electronic signal to the othercollection node during a second portion of the modulation of themodulated light, wherein for each subframe the pattern is used todetermine whether the signal is demodulated by means of the saiddemodulation process or the signal is discarded.
 16. The method of claim14, wherein, the method further comprising projecting a light-patternonto the scene, and the pattern received by the control logic moduledirecting the electronic signal to one of the collection nodes if thelight received at the respective pixel approximately corresponds to oneor more of predetermined light path types associated with that node,wherein the predetermined light path type is selected from a groupcomprises one of consisting of a direct light path, an indirect lightpath, and a specular light path.
 17. The method of claim 10, wherein thelight received from the scene comprises photometric stereo lightillumination conditions from one or more light sources, and theelectronic signal is directed by the pattern to one of the collectionnodes for each respective illumination condition, the method furthercomprising determining surface orientations of one or more objects inthe scene based on intensity of light received.
 18. The method of claim14, wherein the light received from the scene comprises structured lightillumination conditions, and the electronic signal is directed by thepattern to one of the collection nodes for each respective illuminationcondition, the method further comprising determining depth to one ormore objects in the scene from intensity of light received viatriangulation with pixels at the light source and pixels at the imagesensor.
 19. The method of claim 14, wherein each of the one or morecollection nodes receive electronic signals associated with a group ofone or more pixels.
 20. The method of claim 14, wherein the patternprevents a subset of the array of pixels from registering light receivedfrom the scene.
 21. The method of claim 14, wherein the one or morecollection nodes comprises, for each pixel, a first type of collectionnode and a second type of collection node, and wherein the patterndirects the electronic signals received from a first subset of the arrayof photosensitive receptors to a subset of the first type of collectionnodes, and from a second subset of the array of photosensitive receptorsto a subset of the second type of collection nodes.
 22. The method ofclaim 14, wherein the one or more collection nodes comprises, for eachpixel, a first type of collection node, a second type of collectionnode, a third type of collection node, and a fourth type of collectionnode, and wherein the pattern directs the electronic signals receivedfrom a first subset of the array of photosensitive receptors to a subsetof the first type of collection nodes, from a second subset of the arrayof photosensitive receptors to a subset of the second type of collectionnodes, from a third subset of the array of photosensitive receptors to asubset of the third type of collection nodes, and from a fourth subsetof the array of photosensitive receptors to a subset of the fourth typeof collection nodes.
 23. The method of claim 22, wherein the lightreceived from the scene comprises temporally modulated light from alight source, wherein the first type of collection node and the secondtype of collection node comprise a first pair of collection nodes andthe third type of collection node and the fourth type of collection nodecomprise a second pair of collection nodes, the system furthercomprising a processor to determine time-of-flight of the modulatedlight by measuring phase differences between the modulated light at thelight source and the light received at the photosensitive receptor, theelectronic signal directed to one of the collection nodes in either thefirst pair or the second pair during a first portion of the modulationof the modulated light and the electronic signal directed to the othercollection node in the same pair during a second portion of themodulation of the modulated light, wherein for each subframe the patterndirects whether the signal is demodulated in the first pair ofcollection nodes or the second pair of collection nodes, and where thecollection nodes in the other pair of collection nodes act as twoadditional signal collection nodes.